I wrote a book. This should probably be an article, I have bust it up into two posts.
Let me start out by quoting my Dad:
"There are three things in life that Man will never understand: Economics, Batteries, and Women."
With that as the philosophical groundwork for my comments, here we go:
The vector sum of everything I've read on de-sulfur-ization of batteries is zero. There is some valid chemistry there regarding hi current pulses for removing lead sulfate crystals from the plates. All batteries slowly develop the lead crystals. Their formation both insulates small microscopic sections of the plates and depletes the lead as they sluff off and fall to the bottom of the battery. And there are probably batteries that are just a little bad that can be helped by this process. But my take on this is that if you keep the battery charged enough it's not a problem. The worst thing for a battery is one that is allowed to loose it's charge (through self discharge or user use) and then just sits there, and that's worse if it too hot or too cold. Deep cycle batteries just have different plate construction that has more room between the plates for the crystals and a bigger area in the bottom to catch them.
Electronically detecting if a battery has too much lead sulfate is tricky. As the plates deteriorate, the effective resistance of the battery goes up. The problem is that a small battery, like a motorcycle battery, has a higher effective resistance than a larger tractor battery. And that resistance varies from battery to battery and production run to production run. I built a trickled charger and tester into a device I built (home automation system battery backup). Trying out various gel cells (sealed lead acid battery with the sulfuric acid suspended in a gel), there was no set threshold that worked. I ended up with an algorythm where you "promise" the battery is charged and then I put a small load on it and measure the voltage drop. We're talking small drops in voltage like .050 volts on the small 20 mA load. If that drop triples, the battery is bad. There's more to it than that, but you get the idea. I also have to wait a few days on my charger so the battery can reach it's ultimate at rest voltage. So I don't really understand how some of these units can figure out that a battery is in trouble just by hooking up to it, even if you specify the amp hour rating of the battery.
So with all that said, and mindful of my Dad's disclaimer, I'm not going to worry about lead sulfate. By the time it's a problem, it's time for a new battery.
I got so annoyed at battery things that I build my own charger years ago. It can output up to 5 amps of current, and the output voltage never exceed 13.7 volts. You can short it out (it has foldback current limiting), and you can back feed it (if it's connected to a battery and you unplug it it's OK). Wiring it in reverse pops a fuse which you then have to change. It was great for ham radio rigs that just need 20 amps on transmit.
Now the 13.7 volts is semi magic. Any voltage of 13.8 volts causes electrolysis in a lead acid battery- you start turning the water in the battery into hydrogen and oxygen gas. Now you see a lot of equipment bring a battery up to 14 volts or so when running, and that's OK _if_ the battery needs charging. If it is fully charged, then you start to create the gas (or "boil off" as it is often called). The reason you need the higher voltage is this:
Remember that the battery has an equivalent series resistance? You can think of this as the resistance of all the metal (lead in the plates, steel in the posts) of the pieces that make the battery. Next remember ohms law where:
voltage = current X resistance
Rearrange this and you get:
current = voltage / resistance
Now since that battery has some internal resistance, the only way to pump current into it is to have a voltage difference between the voltage of the battery and the voltage of the charging source. The charger has to be at a higher voltage than the battery. We measure voltage because it's easy (it's an across the terminals, easy to do thing) but current gets the job done. Those little electrons zipping through the lead plates makes the chemical reaction that charges the battery. So in order to charge the battery in some reasonable amount of time, we have to up the voltage so we have some current to charge the battery.
If we run our equipment long enough, the battery is charged and the higher-than-13.8 volt alternator voltage is now starting to "boil off" the battery. So the alternator voltage is a bit of a guess and as long as the battery gets charged we take a bit of abuse when we continue to charge it.
All of the above points out an interesting difference between charging, trickle charging, and maintaining a battery. When we charge a battery, we want to get it up and going in a hurry. So we put lots of voltage on it to get high currents so it charges. If you leave the charger on too long, you can really remove some water through electrolysis. You also loose some water because you are heating up the battery and it can evaporate. The semi-sealed cell caps help prevent this, but it is still happening.
When we trickle a battery, we put a smaller voltage on there that will "top off" the battery, and if the trickle charger is left on for too long there isn't too much damage. We sacrifice speed for tolerance of user error.
When we maintain a battery, in an ideal world, we would never exceed the 13.8 volt limit once the battery was charged. "once the battery was charged" is the problem. When you're pumping current into a battery and remove it, you will see a higher voltage at the time you remove the current than you will after a little time has passed. And all that depends on the size and condition of the battery. Figuring out that a battery is fully charged while you're charging it is a very tricky business. Your cell phone is a closed controlled environment yet the battery indicator is marginal at best. A "works on any battery" charger-maintainer device is a much harder problem.
These three flavors of battery charging devices are implemented differently. The charger can be a cheap transformer with diodes that just blasts current into the device. It can have a switch that selects from different taps on the transformer producing different voltages that make the "2 or 10 amp" charge.
A trickle charger can just be a much smaller transformer with diodes, and it might have a simple regulator (such as a shunt regulator) to make sure it doesn't put too much current in the battery.
The battery maintainer needs to have a regulated clean DC output. The more current it outputs, the more it will cost.
So my home brew charger when put on a battery will output a reasonable amount of current if the battery is at 12V. As the voltage comes closer to the output of the charger (13.7 volts) the current goes down. This is a classic "Walking towards the wall" problem: "You are a distance from the wall, you can take a step that is half of that distance. Do you ever reach the wall? No." So my batteries sit at about 13.65 volts or so. The leakage current on the batter cause that effect. This also gives us yet another 80-20 rule (the 1st one being that in any volunteer organization, 20 percent of the people do 80 percent of the work). 80% of the charging is done in the 1st 20% of the time.
Next post is part 2...
